This invention relates to a system for controlling the time at which a durable item used in a manufacturing process is requalified for use and particularly to such a system in which the time at which such durable item is requalified is determined by the occurrence of one or more of a predetermined number of definable events.
Within manufacturing environments today, durable items (that is, resources that are reused during the manufacturing process) are key elements in the production process. These durable items are subject to damage during use and, therefore, it has become the practice to requalify such durable items at specific time intervals.
A specific example of such a durable item would be a photomask (called a reticle) which is used in a lithography tool of a semi-conductor manufacturing facility. For the case of reticles, a requalification is typically initiated at a pre-determined time interval after its introduction into the manufacturing process to ensure that the reticle is viable for use in the process. This requalification process typically has overhead associated with it, which means that the lithography tool is used for requalification rather than making product during requalification. This conventional method of requalification results in the reticle being removed from the production process after its expiration time, and is thus unavailable for use in manufacturing for the entire lifetime of the requalification job.
In accordance with the present invention, requalification of a durable item used in a manufacturing process is initiated prior to the durable item""s expiration. The system of this invention includes a first counter for counting the occurrences of first events to provide a first counter count, a device for determining if the first counter count exceeds a warning level, a device for determining if said first counter count is less than a limit level and a requalification device for initiating requalification of said durable item when the warning level is reached, but before the limit level is reached.
In a preferred embodiment of this invention the system also includes an apparatus for using the durable item in the manufacturing process and apparatus for determining if the durable item is fit for further use. In a further embodiment, the system also includes an apparatus, responsive to a determination that the durable item is fit for use, for resetting the first counter.
The system can also be used if the durable item also expires after a second predetermined number of second events. In such circumstances the system also includes a second counter for counting the occurrences of the second events to provide a second counter count; a device for determining if the second counter count exceeds a second warning level; a device for determining if the second counter count is less than a second limit level; and the requalification device also initiates requalification of the durable item when the warning level is reached, but before the limit level is reached.